Electrical control circuitry for use in combustion supervision systems



March 18, 1969 P. GIUFFRIDA ELECTRICAL CONTROL CIRCUITRY FOR USE IN COMBUSTION SUPERVISION SYSTEMS Filed June 22, 1967 Ow kO@ ON mQZOOmm O Ill... ||H. N if 1Q lml MW ITIIII N f m mko/.p200 mm2; M EOM. QM,N Nlm United States Patent O M 3,433,572 ELECTRICAL 'CONTROL CIRCUITRY FOR USE IN COMBUSTION SUPERVISION SYSTEMS Philip Giuffrida, North Andover, Mass., assignor to Electronics Corporation of America, Cambridge, Mass., a corporation of Massachusetts Filed June 22, 1967, Ser. No. 647,980

U.S. Cl. 431-31 12 Claims Int. Cl. F23n 5 08, 5 /20 ABSTRACT OF THE DISCLOSURE A combustion supervision system includes a control relay which energizes dame scanner electronics, a blower motor and a timer motor in response to a call for heat. The scanner electronics include a Geiger-Mller ultraviolet radiation detector which in response to fiame applies pulse signals to the input circuit of a Type 3N84 silicon controlled rectifier (SCR). The SCR is energized from an AC source, so that it normally becomes nonconducting during alternate half cycles. During` a prepurge cycle controlled by the timer motor that timer closes contacts to connect an RC circuit across the SCR which circuit, so connected, prevents the SCR from ceasing conduction during those alternate half cycles. Should the SCR 'become conductive while the RC circuit is connected, a safety lockout switch will operate which must be man- -ually reset in order to restart the system. If the SCR does not become conductive, the timer opens the connection between the RC circuit and the SCR prior to the ignition cycle and controls that cycle and the subsequent combustion cycle to establish fiame in the combustion chamber which is supervised by the radiation detector.

Summary j invention This invention relates to electrical control circuitry and more particularly to control circuitry particularly adapted for use in combustion supervision systems.

In combustion supervision systems a cycle for purging the combustion chamber is frequently provided prior to the ignition cycle and during that purge cycle it is desirable to test the proper operation of the flame sensor and its associated circuitry. One or more of a variety of arrangements are presently utilized for performing such tests but most of those arrangements will not lock out the supervised combustion system in response to a detected intermittent false flame condition during the purge cycle. Such lockout has heretofore been accomplished by using a magnetic lockout switch, a relatively expensive device, and it is an object of this invention to provide a simplified yet reliable lockout circuit which operates in response to an intermittent false flame condition prior to initiation of an ignition cycle.

Another and more generalobject of this invention is to provide novel and improved combustion supervision apparatus for testing the proper operation of the flame sensor and its associated circuitry during the purge cycle.

Another object of the invention is to provide a novel and improved circuit arrangement for use in combustion supervision systems for checking in a coordinated and reliable .manner the proper operation of the fiame sensor prior to initiating the fuel burnin-g sequence.

Still another object of the invention is to provide a novel and improved circuit arrangement for use in combustion supervision systems which responds to indicated false flame condition prior to the flame initiation cycle and disables the operation of the burner until manual supervision of the control system has been utilized.

Another object of the invention is to provide a novel and improved circuit arrangement for use in combustion 3,433,572 Patented Mar. 18, 1969 ICC supervision systems which responds to even a transient false fiame indication prior to the flame initiation cycle in a reliable and yet economical manner.

Still another object of the invention is to provide a clrcuit arrangement for responding to even a transient false flame indication prior to the iiame initiation cycle, which circuit arrangement requires only minor modification of available combustion supervision circuit arrangements.

In accordance with the invention, there is provided a combustion supervision circuit for use in a combustion control system that includes a fuel control element; an ignition control element; a scheduler for operating components of the combustion control system to provide in sequence an initial (typically a purge) inter-val, an ignition interval, and a combustion interval; a flame detector; and circuitry responsive to the flame detector for providlng an indication of the flame condition in the supervised combustion chamber. The circuitry normally has monostable characteristics so that said circuitry provides an indication of flame only if the flame detector is sensing a flame condition and is characterized by the provision of an arrangement `for converting said circuitry from its normal monostable mode to a bistable mode, and a control for operating said arrangement to convert said circuitry to bistable mode during the initial interval in the operation of the system and returning said circuitry to its monostable mode prior to initiation of the ignition interval by the scheduler.

In a particular embodiment of the invention an ultraviolet radiation sensor is utilized as the fiame detector and the output pulses from that sensor in response to detected ultraviolet radiation from flame operate a controlled rectifier circuit to energize a flame relay. In normal (monostable) mode the controlled rectifier circuit will maintain the flame relay in picked up condition only if ultraviolet radiation from a flame is continually sensed by the sensor. Connected across the main circuit of the controlled rectifier is a mode converting circuit which acts to maintain the controlled rectifier in conducting condition once it has been turned on rather than allowing it to release upon absence of a signal at its control electrode. This mode converting circuit is enabled during the purge interval and appearance of a flame signal during that interval causes flame relay to be energized continuously until the main control relay is de-energized in a manner that resets the scheduler and requires manual intervention in order to restart the controlled combustion system.

The invention provides a simple and reliable circuit arrangement which checks the flame sensor and its associated circuitry for false indications of flame (both of the steady state and intermittent types) and upon detection of any such indication causes the circuit to prevent burner operation until manual supervision has occurred.

' Other objects, features and advantages of the invention will be seen as the following description of a particular embodiment progresses, in conjunction with the drawing, in which:

FIG. l is a schematic diagram of a combustion control system constructed in accordance with the invention; and

FIG. 2 is a timing diagram indicating the operation of the scheduler employed in the system shown in FIG. l.

Description of partz'dular embodiment The system shown in FIG. 1 includes terminals 10, 12 for connection to a 230 volt source of electric power. Connected in series with terminal 10 is a limit control switch 14, an operation control switch 16, and a start interlock switch 18. Circuit control elements include a main control relay 20, a flame relay 22 connected in circuit with a silicon control switc-h 24 for operation in response to a signal from ultraviolet radiation dame sensor 26; a burner motor 28 which operates a blower to move air through the combustion chamber; a scheduler in the form of a timer motor 30 which operates timer contacts 30-1- 30-13; a safety lockout actuator 32 which operates contacts 32-1 and 32-2; an ignition control 34; a pilot fuel control 35; a main fuel control 36; and an alarm 38.

The circuit controlling the blower motor 28 and scheduler motor 30 includes double pole switches 20-1 and 20-2 operated by control relay 20, timer contacts 30-1, 30-2 and 30-3, and normally closed flame relay contacts 22-4. A blower energizing circuit is completed from line via timer contacts 30-1 through blower motor 28 to line 12. A timer motor energizing circuit is also completed through timer contacts 30-1, the normally closed control relay contacts 20-2 and 20-1, and the normally closed fiame relay contacts 22-4 to energize timer motor 30. When control relay 20 is energized a circuit bypassing timer contacts 30-1 is completed through the normally open contacts of control relay contacts 20-1 and 20-2. Further a branch timer motor circuit from the burner motor circuit is provided through timer contacts 30-2 and 30-3.

The main control relay energizing circuit is completed through start interlock switch 18, timer contacts 30-4, normally closed lockout contacts 32-1, timer contacts 30-5 to the control relay coil 20. That coil has a tap 40 to which the lockout heater 32 is connected. In addition, the main control relay circuit includes normally closed flame relay contacts 22-1, normally open flame relay contacts 22-2, and timer contacts 30-6.

The fuel and ignition circuitry is energized via control relay contacts 20-3 and either fiame relay contacts 22-3 or timer contacts 30-7 which apply a signal to junction 42. That circuitry further includes, as control elements, timer contacts 30-8, 30-9, 30-10, 30-11, and 30-12.

Alarm 38 is connected between lines 10 and 12 via the normally open contacts 32-2 of the safety lockout switch.

The electronic circuitry and scanner are also energized from junction 42. Connected from that junction to line 12 via capacitor 44 is a primary winding 46 of transformer 48. That transformer has a tapped secondary Winding providing a first section 50 which produces a twenty-two volt output and a second section 52 which produces a six hundred volt output. Tap 54 is grounded and terminal 56 is connected through capacitor 58 to ultraviolet scanner 26 which is of the Geiger-Mller type. Resistor `60 (which may, together with tube 26, be located at a remote location, for example, in the wall of the combustion chamber to be supervised) couples the sensor 26 to inductor 62 which has output lines 64, 66 coupled through diodes 68 (connected together at common junction 70) which provide an input signal to the input network connected to the controlled rectifier 24. One end of inductor 62 is connected through capacitor 72 to the ground bus 7-4 while a second tap 76 is directly grounded.

The input network to the controlled rectifier includes three capacitors 80, 82 and 84 and three resistors 86, 88 and 90. The signal generated by this timing and pulse shaping network is applied to control electrode 92 which is biased via resistor 94 and diode 96 from the twenty-two volt potential supplied at terminal 98 of transformer secondary section 50. The controlled rectifier 24 has a main circuit which is connected to coil 22 of the flame relay. A diode 100, connected across coil 22, provides a circuit for maintaining current fiow through coil 22 during each half cycle when rectifier 24 is non-conductive. This circuit is connected directly across the secondary winding 50. In addition, a pulse spike suppression capacitor 102 is connected across that winding and a diode 104 provides a DC signal to the controlled rectifier. A mode 'conversion circuit connected across the controlled rectifier includes a resistor 108, capacitor 110 and timer contacts 30-13. As will be noted from the com; ponent values indicated on the drawing, the time constant of this mode conversion circuit is sufficiently great so that when contacts 30-13 are closed the DC signal applied to the main circuit of the controlled rectifier is not interrupted periodically as is the case of the circuit when con tacts 30-12 are open.

When power is applied to terminals 10, 12, and control switches 14, 16, and 18 are closed, power is applied through timer contacts 30-4, the normally closed lockout switch contacts 32-1, the normally closed fiame relay contacts 22-1, the safety cutout heater 32 and via the tap 40 the lower section 0f the main control relay winding 20 so that the main control relay is energized and operates contacts 20-1, 20-2 and 20-3. It will be noted that this energizing circuit provides a check for the proper condition of the iiame relay (via normally closed contacts 22-1) and checks the continuity of the heater 32. The closing of normally open control relay contacts 20-1 and 20-2 completes a circuit to energize the blower motor 28 (initiating a purge cycle), and also through timer contacts 30-2 and flame relay contacts 22-4 to start the timer motor 30. The closing of contacts 20-3 completes a circuit paralleling start interlock 18 and timer contacts 30-4, maintaining energization of the control relay 20 after timer contacts 30-4 open (in five seconds) provided purge air fiowing in the combustion chamber has closed contacts 28-1. After two seconds of timer motor operation contacts 30-1 will close, completing a holding circuit bypassing the now closed control relay contacts 20-1 and 20-2. After five seconds of operation the start interlock timer contacts 30-4 open so that energization of the control relay is maintained solely through its contacts 20-3.

At seven seconds contacts 30-13 close, converting the fiame sensor circuitry from its monostable mode t0 its bistable mode. In other words, the controlled rectier 24, in normal mode, is maintained conducting only if flame sensor 26 continually provides a flame present signal. In the bistable mode however once controlled rectifier 24 is placed in conducting condition, for example due to a defect in the fiame sensor (even a transient condition of short duration), it remains in conducting condition. The purge cycle, initiated by the energization of blower motor 28, produces air flow in the combustion chamber which closes blower responsive contacts 28-1. (Should there be no air flow in the combustion chamber, the control relay holding circuit of contacts 20-3 is not maintained.) This purge cycle and testing of the operability of the sensor and flame relay circuitry continues for twenty-six seconds at which time contacts 30-13 open so that the flame relay circuitry reverts to its monostable mode. (Should a check sequence simulating flame be desired during the purge cycle, such sequence can be incorporated either before or after the bistable mode interval.)

At the end of the bistable mode interval, a circuit around normally closed contacts 22-4 of the fiame relay is completed by the closing of timer contacts 30-3; and at the same time, by closing of timer contacts 30-5, a circuit is completed to energize the entire winding of control relay 20 in what may be termed autotransformer action increasing the current fiow through heater 32 via timer contacts 30-5 and flame relay contacts 22-1 to operatively energize that heater.

An ignition sequence is initiated by the coordinated operation of contacts 30-7 to 30-12. Contacts 30-9 close at twenty-five seconds and contacts 30-8 close at thirtyfive seconds completing a circuit at that time to energize the ignition control 34 and the pilot fuel control 35. Pilot fiame should be established and be sensed by sensor 26 to energize the fiame relay 22 which closes contacts 22-2 and 22-3 and opens contacts 22-1 and 22-4. After three seconds of trial ignition contacts 30-7 open so that the flame condition can be maintained only through the closed ame relay contacts 22-3. Ignition terminates after thirtynine seconds and a transfer to the main fuel line occurs at forty-tive seconds by the closing of contacts 30-12.

The fiow of pilot fuel is terminated at forty-nine seconds by the opening of contacts 30-11.

When fiame relay 22 was energized, contacts 22-1 were opened (terminating current ow through heater 32); and the timer motor 30 stops with the opening of timer contacts 30-2 at fifty-two seconds. The system remains in operation until operating control switch 16 is opened which de-energizes the main fuel valve control 36, control relay 20 and the scanner electronics. Contacts 20-1 and 20-2 return to their normally closed position and complete a circuit through the now closed flame relay contacts 22-4 to start the timer motor which runs for eight seconds until contacts 30-1 open completing the cycle ofthe combustion control system.

Should a flame signal be generated during the bistable mode interval (7-33 seconds) the flame relay is energized and remains energized whether or not that signal is transient or continuous. A circuit for energizing the complete relay coil 20 is established through the now closed ame relay contacts 22-2 and current flows in the lockout heater 32 of magnitude sufficient to operate and open contacts 32-1 after a short time. Also an alarm is signalled by the closing of contacts 32-2. The control relay coil is de-energized, opening contacts 20-3 so that no ignition sequence may be initiated.

The control relay contacts 20-1 and 20-2 return to their normally closed position, and as the flame relay 22 has been de-energized (through the opening of contacts 20-3), a timer motor circuit is established through timer contacts 30-1, control relay contacts 20-1 and 20-2 in their normally closed position, and normally closed flame relay contacts 22-4. This circuit remains completed and the timer motor runs until timer contacts 30-1 open at sixty seconds. The system thus is reset without initiation of fiame in a safe condition, and cannot be restarted until the safety lockout switch 32 is manually reset.

If no false flame signal is generated during the bistable mode interval, and ignition sequence is initiated at thirtyfive seconds and if the ame relay 22 is picked up in response to detection of flame prior to thirty-eight seconds the combustion cycle is commenced and maintained, in the absence of liame failure, until the call for heat terminates (indicated by the opening of switch 16). Should the flame fail during this period, however, the lockout heater 32 is energized and operates to open contacts 32-1 after a short time. The system is then shut down in safe condition as described above and an alarm 38 energized (via contacts 32-2) such that manual intervention is required to restart the system.

While a particular embodiment of the invention has been shown and described, various modifications thereof will be apparent to those skilled in the art and therefore it is not intended that the invention lbe limitedhto the disclosed embodiment or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What is claimed is:

1. A combustion supervision circuit for use in a combustion control system that includes a fuel control elenient; an ignition control element; a scheduler for operating components of said combustion control system to provide an initial interval, an ignition interval, and a combustion interval; and a llame detector,

said combustion supervision circuit including an indicator responsive to said flame detector for providing an indication of the flame condition in the supervised combustion chamber, said circuit normally having monstable characteristics so that said indicator provides an indication of flame only if said fia-me detector is sensing a fiame condition, 'and safety circuit means responsive to said indicator for shutting down said system in safe condition,

characterized by the provision of first means for converting said flame detector responsive circuit from its normal monostable mode to a bistable mode in which said indicator continues to provide an indication of flame after said flame detector provides a transient ame condition signal, and control means for operating said first means to convert said flame detector responsive circuit to said bistable mode during said initial scheduler interval and to return said flame detector responsive circuit to its monostable mode prior to initiation of said ignition interval by said scheduler, said safety circuit means shutting said system down in safe condition when said indicator provides a fiame indication during said initial scheduler interval.

2. The combustion supervision circuit as claimed in claim 1 wherein said ame detector responsive circuit includes a controlled rectifier circuit normally arranged to be periodically rendered non-conductive and said first means includes a circuit for maintaining said controlled rectifier circuit in conductive condition after said controlled rectifier circuit has been placed in conductive condition.

3. The combustion supervision circuit as claimed in claim 2 wherein said controlled rectifier circuit includes an alternating current energizing source and said maintaining circuit includes a resistance capacitance circuit having a time constant sufficiently great to prevent the controlled rectifier from being rendered non-conductive during alternate half cycles of said energizing source.

4. The combustion supervision circuit as claimed in claim 3 wherein said resistance capacitance circuit is connected across said controlled rectifier by said scheduler during said initial interval.

5. The combustion supervision circuit as claimed in claim 1 wherein said ame detector is of the Geiger- Mller type.

6. A combustion control system comprising a fuel control element; an ignition control element; a scheduler for operating components of said combustion control system to provide an initial interval, an ignition interval, and a combustion interval; a fiame detector; a circuit including an indicator responsive to said flame detector for providing an indication of the liame condition in the supervised combustion chamber, said circuit normally having monostable characteristics so that said indicator provides an indication of dame only if said fiame detector is sensing a fiame condition; safety circuit means responsive to said indicator for shutting down said system in safe condition, mode converting means for converting said circuit from its normal monostable mode to a bistable mode in which said indicator continues to provide an indication of flame after said flame detector provides a transient fiame condition signal, and control means for operating said converting means to convert said circuit to bistable mode during said initial scheduler interval and to return said circuit to its monostable mode prior to initiation of said ignition interval by said scheduler, said safety circuit means shutting said system down in safe condition when said indicator provides a flame indication during said initial scheduler interval.

7. The combustion control system as claimed in claim 6 wherein said ame detector is of the Geiger-Mller type.

8. The combustion control system as claimed in claim 7 and further including a blower for producing a flow of air through the combustion chamber supervised by the combustion control system during said initial scheduler interval to provide a purge cycle and wherein said mode converting control mean is operative in response to said scheduler during said purge cycle.

9. The combustion control system as claimed' in claim 7 wherein said safety circuit means includes a heater, contacts adapted to move from a first position to a second position in response to electrical current flow through said heater, and a manual operator for resetting said contacts to said first position.

10. The combustion control system as claimed in claim 9 wherein said llame detector responsive circuit includes a controlled rectilier` circuit normally arranged .,to be periodically rendered non-conductive and said mode converting means includes a circuit for Imaintaining said controlled rectifier circuit in conductive condition after said controlled rectifier circuit has been placed in conductive condition.

11. The combustion control system as claimed in claim 10 wherein said controlled rectifier circuit includes an alternating current energizing source and said maintaining circuit includes a resistance capacitance circuit having a time constant sufficiently great to prevent the controlled rectier from being rendered non-conductive during alternate half cycles of said energizing source.

12. The combustion control systemas claimed in claim 15 431-69 11 vv-herein saidV resi'stmicefcapacitance.circuitisvcori-v nected across said -controlledf rectifierbyf said 'scheduler `during lsaid purge cycle. o Y. n t i Y l lefei-"eric*esili*Cited 'I l l UNITED STATES, PATENTS '3,266,551 s/1966 Giuffrida.'

13,324,927 6/,1967 staring. l l 3,343,585 o 9/1 9'67 iacleiug'rrgl JAMES W. 'WEsrHAvErg Primaryl Examiner.

Us] cl. X1k. i 

